1. Field of the Invention
This invention relates to electronic devices, especially organic electronic devices, and methods for forming such devices.
2. Description of the Related Art
Semiconducting conjugated polymer thin-film transistors (TFTs) have recently become of interest for applications in cheap, logic circuits integrated on plastic substrates (C; Drury, et al., APL 73, 108 (1998)) and optoelectronic integrated devices and pixel transistor switches in high-resolution active-matrix displays (H. Sirringhaus, et al., Science 280, 1741 (1998), A. Dodabalapur, et al. Appl. Phys. Left. 73, 142 (1998)). In test device configurations with a polymer semiconductor and inorganic metal electrodes and gate dielectric layers high-performance TFTs have been demonstrated. Charge carrier mobilities up to 0.1 cm2Ns and ON-OFF current ratios of 106-108 have been reached, which is comparable to the performance of amorphous silicon TFTs (H. Sirringhaus, et al.; Advances in Solid State Physics 39, 101 (1999)).
One of the advantages of polymer semiconductors is that they lend themselves to simple and low-cost solution processing. However, fabrication of all-polymer TFT devices and integrated circuits requires the ability to form lateral patterns of polymer conductors, semiconductors and insulators. Various patterning technologies such as photolithography (WO 99/10939 A2), screen printing (Z. Bao, et al., Chem. Mat. 9, 1299 (1997)), soft lithographic stamping (J. A. Rogers, Appl. Phys. Lett. 75, 1010 (1999)) and micromoulding (J. A. Rogers, Appl. Phys. Lett. 72, 2716 (1998)), as well as direct ink-jet printing (H. Sirringhaus, et al., UK 0009911.9) have been demonstrated.
Many direct printing techniques are unable to provide the patterning resolution that is required to define the source and drain electrodes of a TFT. In order to obtain adequate drive current and switching speed channel lengths of less than 10 μm are required. In the case of inkjet printing this resolution problem has been overcome by printing onto a prepatterned substrate containing regions of different surface free energy (H. Sirringhaus et al., UK 0009915.0).
In U.S. patent application No. 60/182,919 a method is demonstrated by which an inorganic metal film on top of a polymer support can be microcut by solid state embossing (N. Stutzmann et al., Adv. Mat. 12, 557 (2000)). A “hard” master containing an array of sharp, protruding wedges is pushed into a polymer supported metal film at elevated temperatures. For a semicrystalline polymer, such as poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP), polyethylene (PE), or poly(ethylene terepthalate) (PET), the embossing temperature is above the glass transition of the polymer, but below its melting temperature. In the case of an amorphous polymer such as atactic polystyrene (PS) or poly(methylmethacrylate) (PMMA) temperatures around the glass transition are used. During the embossing the master penetrates into the metal-polymer structure and plastic flow of material occurs away from the wedge. If the indentation depth is larger than the metal film thickness a groove is generated which cuts through the metal film. In the remaining areas the integrity of the metal-polymer layer structure is preserved because embossing is performed in the solid state and plastic flow mainly occurs laterally.